The central role of the long form of amyloid beta-peptide, in particular Aβ(1-42), in Alzheimer's disease has been established through a variety of histopathological, genetic and biochemical studies. See Selkoe, D J, Physiol. Rev. 2001, 81:741-766, Alzheimer's disease: genes, proteins, and therapy, and Younkin S G, J Physiol Paris. 1998, 92:289-92, The role of A beta 42 in Alzheimer's disease. Specifically, it has been found that deposition in the brain of Aβ(1-42) is an early and invariant feature of all forms of Alzheimer's disease. In fact, this occurs before a diagnosis of Alzheimer's disease is possible and before the deposition of the shorter primary form of A-beta, Aβ(1-40). See Parvathy S, et al. Arch Neurol. 2001, 58:2025-32, Correlation between Abetax-40-, Abetax-42-, and Abetax-43-containing amyloid plaques and cognitive decline. Further implication of Aβ(1-42) in disease etiology comes from the observation that mutations in presenilin (gamma secretase) genes associated with early onset familial forms of Alzheimer's disease uniformly result in increased levels of Aβ(1-42). See Ishii K, et al Neurosci Lett. 1997, 228:17-20, Increased A beta 42(43)-plaque deposition in early onset familial Alzheimer's disease brains with the deletion of exon 9 and the missense point mutation (H163R) in the PS-1 gene. Additional mutations in the amyloid precursor protein APP raise total Aβ and in some cases raise Aβ(1-42) alone. See Kosaka T, et al Neurology, 48:741-5, The beta APP717 Alzheimer mutation increases the percentage of plasma amyloid-beta protein ending at A beta42(43). Although the various APP mutations may influence the type, quantity, and location of Aβ deposited, it has been found that the predominant and initial species deposited in the brain parenchyma is long Aβ (Mann). See Mann D M, et al Am J Pathol. 1996, 148:1257-66, Predominant deposition of amyloid-beta 42(43) in plaques in cases of Alzheimer's disease and hereditary cerebral hemorrhage associated with mutations in the amyloid precursor protein gene.
In early deposits of Aβ, when most deposited protein is in the form of amorphous or diffuse plaques, virtually all of the Aβ is of the long form. See Gravina S A, et al J Biol Chem, 270:7013-6, Amyloid beta protein (A beta) in Alzheimer's disease brain. Biochemical and immunocytochemical analysis with antibodies specific for forms ending at A beta 40 or A beta 42(43); Iwatsubo T, et al Am J Pathol. 1996, 149:1823-30, Full-length amyloid-beta (1-42(43)) and amino-terminally modified and truncated amyloid-beta 42(43) deposit in diffuse plaques; and Roher A E, et al Proc Natl Acad Sci USA. 1993, 90:10836-40, beta-Amyloid-(1-42) is a major component of cerebrovascular amyloid deposits: implications for the pathology of Alzheimer disease. These initial deposits of Aβ(1-42) then are able to seed the further deposition of both long and short forms of Aβ. See Tamaoka A, et al Biochem Biophys Res Commun. 1994, 205:834-42, Biochemical evidence for the long-tail form (A beta 1-42/43) of amyloid beta protein as a seed molecule in cerebral deposits of Alzheimer's disease.
In transgenic animals expressing Aβ, deposits were associated with elevated levels of Aβ(1-42), and the pattern of deposition is similar to that seen in human disease with Aβ(1-42) being deposited early followed by deposition of Aβ(1-40). See Rockenstein E, et al J Neurosci Res. 2001, 66:573-82, Early formation of mature amyloid-beta protein deposits in a mutant APP transgenic model depends on levels of Abeta(1-42); and Terai K, et al Neuroscience 2001, 104:299-310, beta-Amyloid deposits in transgenic mice expressing human beta-amyloid precursor protein have the same characteristics as those in Alzheimer's disease. Similar patterns and timing of deposition are seen in Down's Syndrome patients in which Aβ expression is elevated and deposition is accelerated. See Iwatsubo T, et al Ann Neurol. 1995, 37:294-9, Amyloid beta protein (A beta) deposition: A beta 42(43) precedes A beta 40 in Down syndrome.
Accordingly, selective lowering of Aβ(1-42) thus emerges as a disease-specific strategy for reducing the amyloid forming potential of all forms of Aβ, slowing or stopping the formation of new deposits of Aβ, inhibiting the formation of soluble toxic oligomers of Aβ, and thereby slowing or halting the progression of neurodegeneration.